No hybrid needed: Tips for more mpg

ROAD WARRIOR

Q: With the high price of gas these days, I've been able to increase the mileage on my 2002 Hyundai Accent by about 10 percent (from 34 to 37 miles per gallon) by coasting ("freewheeling"). On a slight downgrade, I throw it into neutral and coast. The car will maintain and sometimes even increase its speed. (On steep declines that require braking there is no advantage to coasting.) I also do some "pulse and glide" driving. By my calculations, my Accent coasting at 30 mph yields 100 mpg, and at 60 yields 200 mpg. Since the car uses a constant amount of fuel per hour when idling, the faster you coast, the better. I conservatively calculate that my car uses 0.3 gallons per hour when coasting, and it could be less.

— Ed Sokalski, Salisbury Township

A: Gas prices have leveled off and declined a bit since your comments rolled into the email garage three weeks ago, Ed, but they're still hovering in the hefty $3.70 range, depending on the grade.

I'm not sure how you arrived at the 0.3 gallons per hour figure, but it seems pretty close to an average for passenger vehicles. Estimates range from below 0.2 gph to more than 1 gph, and of course, the actual value differs from car to car. A police officer wrote on one website that his 4.3-liter V8 patrol-car engine uses 0.5 gph when idling "with the heater on, the four-ways working and [the engine] powering 600 watts of flash-bar."

The exact amount of fuel burned at idle doesn't really matter though, according to a study by Popular Mechanics magazine. In his July 2010 story on the experiment, Mike Allen contends that coasting in neutral actually reduces gas mileage.

The magazine connected measuring devices to the test car's fuel injectors, revealing that while coasting with the car in gear, "there is no fuel injected at all" into the engine, which is turning at the behest of wheels and running gear, but not consuming any fuel.

When you throw it into neutral, you're using 0.3 gph or maybe less — very little gas, indeed. But even if it's 0.001 gph, it's more than zero, so you're actually wasting fuel by putting the car in neutral and breaking the connection that keeps the engine "running" without fuel.

Some people contested Allen's experiment in responses to the magazine's website. Technical assumptions were challenged, among other issues. The article and comments are still posted at popularmechanics.com, so fellow warriors can judge for themselves. I couldn't reach Allen to discuss these matters, but I find his conclusions pretty convincing.

Allen says it's actually dangerous to coast in neutral because a car's handling characteristics change when the link between engine and drivetrain is broken. I'm not sure I buy that, though if the engine would stall, power steering and power braking would fail, which could be very dangerous. He also says you might need to accelerate quickly in an avoidance maneuver; I guess that's possible, but it's too unlikely to warrant consideration. I've heard that as justification for "needing" more horsepower, too, and in that application it's totally tailpipe exhaust. An overload of horsepower is far more likely to boost the danger level than widen any safety margin.

I don't doubt that your mileage has increased, Ed, but I suspect coasting hasn't contributed to the gain, at least not by a meaningful amount. You have a good grasp on the wheel of other high-mileage practices, and it could be that other tactics are torquing up your mpg.

Your email included this spot-on advice: "As you know, the best ways to reduce your fuel costs are, in order of benefit, drive less (walk, combine trips, etc.); drive a more fuel-efficient car when you can; drive slower, and avoid 'jackrabbit' starts and stops."

Those are sure-fire spark plugs on the road to optimum mileage. Other helpful tips include lightening the weight and resistance loads by removing empty roof racks and unnecessary items from the trunk or hatch; using cruise control (which maintains a constant speed more effectively than people can, with fewer fuel-wasting adjustments); maintaining proper tire inflation (check the pressure with a gauge; don't rely on the car's monitoring system, which offers worst-case alerts)' and eliminating unnecessary idling.

Yes, the idling issue rears its ugly headliner again — and it's still stuck in controversial gear. The California Energy Commission, among others, recommends that motorists shut off the engine any time they expect to be idling without moving for 30 seconds or more. Some suggest shutting down at the 10-second mark, which I consider excessive, requiring too much re-starting to make sense.